Sound producing instrument and diaphragm therefor



Nov. 13, 195] J. E. PETEK 2,575,293

SOUND PRODUCING INSTRUMENT AND DIAPHRAGM THEREFOR Filed Aug. 27, 1948 2 SHEETS SHEET l lll l W 4f .INVENTOR.

fiEFH E1. PETEH BY I Fl C1. 4

ATTQPNEY I Nov. 13, 195] PETEK 2,575,293

SOUND PRODUCING INSTRUMENT AND DIAPHRAGM THEREFOR Filed Aug. 27, 1948 2 SHEETS--SHEET 2 THlCKNESS (INCHES) 4o 45 5o 55 LONGITUDINAL ARC RADIUS (INCHES) F" 16. IO

INVENTOR. JOSEPH E. PETEK BY 6;. 6. Vim

A TTOPZJEY Patented Nov. 13, 1951 UNITED STATES PATENT OFFICE SOUND PRODUCING INSTRUMENT AND DIAPHRAGM THEREFOR This invention relates to instruments or devices having sound transmitting or producing diaphragms. The invention is shown incorporated in a musical instrument wherein the produced sounds are generated in response to vibrated strings. The invention is disclosed as embodied in a violin as illustrating the preferred application of my invention.

In the fabrication of violins, it has been the practice, so far as I have knowledge, to use special kinds of wood and to select those portions thereof that were devoid of various imperfections and to vary the thickness of the belly and back dependent on the stiffness and weight of the .wood for the purpose of attaining desirable tone qualities.

I have discovered that the tone quality of an instrument can be improved by employing a diaphragm of reduced thickness and having a predetermined degree of arching and a predetermined resonant frequency, the effect of which is to reduce damping and tone distortiomwhereby the produced tones of the instrument are louder, clearer and mor uniform.

One object of the invention is to provide for a sound producing device an improved diaphragm constructed to reduce damping of the vibrations thereof and distortion of the tones.

Another object of the invention is to provide an improved violin or like instrument wherein the belly or both the belly and back are constructed to reduce damping of the vibrations thereof and distortion of the tones when the instrument is played.

Another object of the invention is to provide an improved violin wherein the belly, for a specifled degree of arching and having a resonant frequency corresponding to the musical note BX may be made relatively thin, whereby the tones of the violin are improved with respect to loudness, clearness and uniformity.

' Another object of the invention is to provide in a violin or like instrument an improved belly consisting of a composite member having predetermined arch radii and a predetermined resonant frequency and relatively thin, as compared to a belly formed of solid wood and having the same arch radii and the same resonant frequency, so that an increased amplitude of vibration of the belly, in response to string vibration, takes place when the instrument is played, to provide an improved tone quality.

1 Another object of the invention is to provide in.a violin or like instrument an improved belly consisting of a composite member having a predetermined arch radii and a predetermined resonant frequency capable of vibrating, in response to string vibration when the instrument is played, at amplitudes which produce louder, clearer and more uniform tones, as compared to a violin the belly of which is solid and formed of the selected wood, has the same arch radii and the same resonant frequency.

Another object of the invention is to provide an improved process of fabricating a violin or like instrument, to insure louder, clearer and more uniform tones.

Other objects of the invention will be apparent to those skilled in the art to which my invention relates from the following description taken in connection with the accompanying drawings, wherein Fig. 1 is a plan view of a violin embodying my invention, parts being broken away.

Fig. 2 is a side elevation.

Fig. 3 is a fragmentary section on the line 3-3 of Fig. 1. 1

Fig. 4 is a fragmentary section on the line 44 of Fig. 1.

Fig. 5 is a section on the lin 5-5 of Fig. 3.

Figs. 6, 7 and 8 are sections similar to Fig. 5, but showing modified forms of construction.

Figs. 9 and l0 are diagrammatic views.

. In the drawings, referring particularly to Figs. 1, 2 and 3, l indicates as an entirety a violin having a diaphragm or belly 2, a back 3, sides 4, tail 5, neck 6, bridge 1 and strings 8. The belly .2 and back 3 each have (a) a thickness and curvature longitudinally as later set forth herein and a curvature transversely thereof on arcs of circles, (b) a length of fourteen inches and (c) a maximum width of eight and one-quarter inches. The diaphragm or belly 2 and back 3 are fabricated in the manner later set forth. The belly 2, back 3, sides 4 and neck 6 are formed from selected wood or woods and assembled and glued together and reinforced according to well known practice. The belly 2 and back 3 may be respec tively formed of two composite side-by-side sec tions glued together as practiced by some makers, but eachwill be described herein as consisting of a single fabricated composite wall or member. By preference, the belly and back are of substantially similar construction so that only one of these parts-the bellyand the process of making it will be described, although the inven- 'tion is not to be limited to a construction where both of these parts embody the invention.

I In carrying out my process the first step consists in (a) selecting the wood of which the belly is to be fabricated, as later set forth, (b) predetermining the thickness of the belly at the point engaged by the bridge and (c) predetermining the longitudinal arc radius of the belly.

In selecting the wood, I first cut from each of several available suitable woods a test member having a length of six inches extending parallel to the wood grain and a width of one-half inch extending radially of the growth rings and an initial thickness of inch or more; the thickness of the test members are then gradually reduced until the resonant frequency thereof corresponds to the musical note B above and adjacent to the note A on the musical scale having a resonant frequency of 440 cycles per thickness factor and the product by the coniposite thickness factor of approximately 1.15, this latter factor being the ratio of thickness of a solid belly it formed of the selected wood to the thickness of a belly formed of the selected wood fabricated as hereinafter set forth (see Fig. 9) and the final product determining the thickness value by which to identify on the graph the longitudinal arc radius to be employed for the belly to be fabricated as hereinafter set forth from the selected wood, that is, the wood corresponding to that wood of the primary test member.

Next, the diaphragm or belly 2 is formed of in- ,ner and outer plies 2a, 2b, from the selected wood,

second. The wood of the test member (later reeach ply having a longitudinal arc radius, as rr d t s primary test member") which is above set forth, and an outline and taper patthe thirmest is then selected. j V V tern corresponding to the test diaphragms above Since it i preferred t have a fixed ratio o referred to. In carrying out this step, one ply stiffness to weight in the complete belly which (th outer or pper ply as viewed in these fighas a resonance correspond to e s d mUSiures) is formed preferably with a thickness as cal note B, and it is also preferred to have a determined by the formula for thickness (T 5), fixed stiffn ss, no ma t W at W d is u d, t whereas the other ply is preferably formed with a thickness for the selected wood must be chosen t ickne s equal to that of th upper ply and to give afixed w i ht f r th mp t d l y- I the spacing devices between the plies, which have found that a thickness of .170 inch for a devices preferably have a thickness equal to wood with a density of .245 ounce per cubic inch, TJZT will provide a belly with a satisfactory stifiness, Next, ap roximately of the wood on that constructed as herei af er Set fo t a d arc face of the other ply (the inner ply as viewed in to resonate at the said note B. To determine 30 these figures) which-when assembled with the the thickness of the selected wood which will outer opposed t t inner face of t Provide h desired ifi l the following forlatter, is removed. Such removal consists in remula i usedi moving the wood within the marginal edges of .0 4165 I v 7 the ply along uniformly spaced longitudinal and T=- transverse channels to a depth substantially 1 equal to T-2Tp, such removal providing upwhere T is the sought for or predetermined thickstanding devices 2a: at the inter-sections of the ness and D is the density of the wood expressed channels, which devices Serve S p in the in ounces per cubic inch. The thickness of each compos e e as later Set forth in i yply (hereinafter referred to) is indicated by the 40 side parall l I In f rmi th h n 5' f rm a; above set forth the wood is preferably removed 7 01,225 so as to provide devices that are round in cross T section, each having a diameter of appro imately v of an inch and spaced, center to center, ap- D have the same value as above and the thick- 'Q t I a h 3 the devices ness of the spacing devices (hereinafter referred a l ws n aggered relation, 7 w I I to) is indicatedby the formula: S=T 2Tp. Next, the top surfaces ofthe dev1ces 2x are In determining the longitudinal arc radius, I covered with} u t c e meni a select a suificiently large section of a suitable the two plies are t e l u 1 wood to provide therefroma secondary test mem- Pressure to commslte alaphra'gm or belly;

ber and at least four test diaphragms or bellies having a predetermined outline and taper pattern. The secondary test member, when out, is

similar to the primary test member as to length and width and relation thereof to the grain and growth rings, respectively, with an initial thickness of inch or more, and then its thickness is trimmed down until the member has a resonant frequency corresponding to the said musical note B; also, the four diaphragms or bellies are arched on difierent longitudinal arc radii, for example, 40", 45", 50 and radius, respectively, and transversely curved on arcs of circles, and the thickness of eac until it has a resonant frequency corresponding to the said musical note B. On a graph (Fig. 10) whose coordinates are longitudinal arc radii and thickness in inches and using the above value and the derived thicknesses of the bellies, I I draw a line a on the graph. By determining the ratio of thickness of the secondary test member to that of the primary test member, I obtain the thickness factor" and then multiply the predetermined thickness T of the selected Wood as determined by the foregoing formula by the h thereof is trimmed down The composite member then tested, after positioning the bass bar and cutting of the holes, to determine whether it has a resonant frequency corresponding to the said musical not 'B. If 55 the resonant frequency corresponds to a musical note above or 'below the note B, the foregoing steps must be repeated with the same kind or wood, to fabricate a new belly, which in turn must be tested. 'If the tests show that the resonant 80 frequency is high, the ratio value 1.15 in the formula is increased approximately .02 or .03 of an inch; if the resonant frequency is low; the ratio value 1.15 reduced approximately .02 or .03 of an inch.

"'65 It will be observed that in. carrying out the above steps, those portions of the composite belly (that is, its inner portions) which contribute least to the stiffness thereof have been removed, as shown at 'b in Fig. 9, such removal tending to increase the resonant frequency of the belly, while by employing plies of the thickness hereinbefore referred to, thereby in effect removing wood from the opposite surfaces of the belly, as shown at C in Fig. 9, its resonant frequency is lowered; areco'rdingly, it will be seen that by removing the sava es corporated in position damping of the produced tones will be materially reduced.

, Next, the back is formed according to the steps above referred to, except that its arching and the thickness are modified to provide a slightly' higher resonant frequency and a heavier back,

for example, a thickness and plies having a thickness 5 next, the parts are assembled and secured together according to the well known practice.

omitted, the effect of which is to reduce damping and tone distortion and this in turn insures louder, clearer and more uniform tones. Reducing damping causes all reproduced tones to be louder, but is most effective in the lower frequencies due to their greater amplitudes of vibration; 5

reducing damping also maintains a better intensity balance between the fundamental frequencies of the tones and their accompanying harmonics. This, in effect, reduces distortion of the tones and insures greater uniformity of tone throughout the range of the instrument.

In carrying out the step of fabricating the belly or the back it will be observed that the plies and spacing devices may be formed separately and thereafter assembled into a composite member, this form of construction being shown in Fig. 6, wherein the inner and outer plie are indicated at 2a, 2b, respectively, and the spacing devices at 2x.

spacing devices 2:0 are separate from the plies 2a, 2b, and have a different cross sectional shape, each device shown in Fig. 7 being formed with an annular v-s'haped groove and each device shown in Fig. 8 being hollow from end to end.

In fabricating the belly and back, the plies therefor are cut from the wood so as to dispose the wood grain similarly to conventional practice where the belly is solid. Where the spacing devices are formed separately, they are positioned between the plies so that the grain of the devices is disposed perpendicularly thereto and the chords of the arcs of the growth rings are disposed parallel to the longitudinal axis of the belly.

From theforegoing description it will be ob- 65 served that my invention is applicable to various kinds of woods; that is, it provides an improved quality of tone of a violin having a belly formed of any selected kind of wood, as compared to a violin having a solid belly formed of the same 70 selected kind of Wood.

To those skilled in the art towhich my invention relates, many changes in construction and widely diifering embodiments and applications of the invention will be apparent without departing from the spirit and scope thereof. My disclosures and the description herein are purely illustrative and-not intended to be in any sense limiting.

What I claim is:

l. The herein disclosed process of forming a composite diaphragm for a musical or sound producing instrument to produce a predetermined resonant frequency, which consists in cutting from a selected wood a ply having a predetermined thickness and a predetermined longitudinal arc radius, then in cutting from the selectedwood a separate ply the thickness of which is approximately twice that of the first mentionedply and having a similar longitudinal arc radius, then in removing material from one surface of the last mentioned ply within its marginal edges to a depth of one-half its thickness and along ,4 spaced angularly related portions to form channels within the member and spacers between the channels, then assembling the first mentioned ply and spacers in contact with adhesive between them, and finally applying pressure to the plies.

2. The herein disclosed process of forming a diaphragm for a musical or sound producinginstrument to produce a predetermined thickness and a predetermined resonant frequency, and employing a graph indicating longitudinal arc radii and thicknesses in predetermined units, which process consists first in selecting from a series of primary test members formed of different woods and having the predetermined resonant frequency the wood corresponding to that of the test member that is the thinnest, forming from a suitable wood a secondary test member having the predetermined frequency, determining the thickness factor between the primary and secondary test members, multiplying the thickness factor by the value of the predetermined thickness and by the composite thickness factor to determine the thickness value, determining the longitudinal arc radius of the diaphragm by the radius on the graph for the thickness corresponding to the thickness value and finally forming from the selected wood a diaphragm having the predetermined thickness and determined longitudinal arc radius.

3. The herein disclosed process of forming a diaphragm for a musical or sound producing instrument to provide a predetermined thickness Figs. 7 and 8 show modifications wherein the and a predetermined resonant frequency, and employing a graph indicating longitudinal arc radii and thicknesses in predetermined units, which process consists first in selecting frgm a series of primary test members formed of dinerent woods and. having the predetermined resonant frequency the wood corresponding to that of the test member that is the thinnest, forming from a suitable wood a secondary test member having the predetermined frequency, determining the thickness factor between the primary and secondary test members, multiplying the thickness factor by the value of the predetermined thickness and the value of a solid diaphragm formed of the selected wood and having the same predetermined resonant frequency to determine the thickness value, determining the longitudinal arc radius of the diaphragm by the radius on the graph for the thickness corresponding to the thickness value, forming from the selected wood plies according to the formula having the determined longitudinal arc radii and formula ski -2T and finally assembling the: plies and spacing devices with adhesivehmaterial betweenthem and applying pressure to the plies.

4. A sound transmitting diaphragm. fora musical instrument adapted to produce musical tones in response to string vibrations and. consisting of a single composite member all parts of which are formed of the same kind or wood and havin inner and outer plies, adjacent respective portions.

of: said plies throughout their areas having the same thickness andthe thickness of the plies tapering toward their peripheral marginal edges, portions of the wood between the plies being re movedto increase the ratiooi stiffness to weight of the composite member as compared. to that or. a solid member formed of the same kind of. wood and having the same thickness, to reduce flexing;

of the Wood fibers of the composite member and.

8 formed Qtthesame kinder or and. outer plies and: spaced spacing dos vices: therehetween formed integrally with one oi said plies, any three mutually adjacents'pacing devices of said spaced spacing, devices being in an equilateral triangular relationship to serveto. increase the ratio. of stiffness to weight of the composite member as compared to a solid member formed oi the some kind of wood and having the same thickness to reduce flexing or the wood fibers of the composite member and damping of the vibrations thereof and to increase the loudness, clearness and uniformity of the tones of the instrument when the latter is played.

JOSEPH PETER,

REFERENCES CITED The following references are of record in the tile; of this patent:

STATES PATENTS- Number Name Date 536,081 Howe Mar.v i9, 189,5 1,349,700 Virzi Aug. 17; 1526 1,719,680 Warner J my -2',-. 1929? 1,876,330 Loetscher Sept. 6, i932 FOREIGN PATENTS Number Country Date '3 20,040 H Great Britain Dec. 4, I894 

